#10559463 Migration flow: Remove FTP option from credential form in migration flow

Related to #85704

Proposed Changes

• Remove options for providing FTP credentials from the credential form screen (as this has no appreciable effect on performance).

Testing Instructions

• Navigate to http://calypso.localhost:3000/setup/import-focused/import?siteSlug=ATOMIC_SITE_SLUG
• Fill in a source site you’d like to migrate from, it can be a JN site.
• Make the Jetpack connection if needed and once you land on the You are ready to migrate screen, click Provide the server credentials link.
• Make sure you see SSH/SFTP as the default credential type in the form.
• Make sure the port number is 22.
• When you select credential type dropdown, there will be no FTP option.

Pre-merge Checklist

• Has the general commit checklist been followed? (PCYsg-hS-p2)
• https://wpcalypso.wordpress.com/devdocs/docs/testing/index.md for your changes?
• Have you tested the feature in Simple (P9HQHe-k8-p2), Atomic (P9HQHe-jW-p2), and self-hosted Jetpack sites (PCYsg-g6b-p2)?
• Have you checked for TypeScript, React or other console errors?
• Have you used memoizing on expensive computations? More info in Memoizing with create-selector and Using memoizing selectors and Our Approach to Data
• Have we added the “[Status] String Freeze” label as soon as any new strings were ready for translation (p4TIVU-5Jq-p2)?
• For changes affecting Jetpack: Have we added the “[Status] Needs Privacy Updates” label if this pull request changes what data or activity we track or use (p4TIVU-ajp-p2)?